Plains farmers supported bimetallism because expanding the money supply would create inflation, making it easier for them to pay their debts. Bimetallism describes a monetary standard that accepts both silver and gold and establishes a fixed rate of exchange between the two metals.
Bimetallism was the center of political controversy during the last quarter of the 19th century in America. Farmers were taking out loans to purchase new industrial equipment to streamline their farms' operations and buying more land. However, increased international competition and economic panic during this period depressed prices, making it difficult for farmers to pay off their loans. Therefore, they wanted an increased money supply which would raise the prices of their products and decrease the real value of the money they owed on their mortgage.
They pressed the U.S. government to adopt silver as a monetary metal in addition to gold, believing that this would create the inflation they desired.